Portable devices depend upon batteries as a power source. As the power consumption demands of these electronics devices is continually increasing, so is the need for high capacity batteries with long storage life. Depending upon the chemistry, rechargeable batteries have different characteristics. For example, one of the earliest rechargeable chemistries, Nickel Cadmium (Ni-Cad), is very robust and inexpensive, but has a very poor capacity to weight ratio that results in large bulky batteries. Another later technology, Nickel Metal Hydride (Ni-MH), proved to be smaller, but offered no significant increase in the capacity to weight ratio.
Lithium Ion (Li-Ion) and Lithium Polymer (Li-P) batteries made a substantial leap in energy capacity per unit weight. With the advent of Li-Ion/Li-P cells, batteries became much smaller with greater storage capacities. The downside of Li-Ion/Li-P, however, involves safety. If Li-Ion/Li-P batteries are charged improperly or over charged, they can rapidly release gas at excessive temperatures, which can cause fire or explosion. Therefore, Li-Ion/Li-P battery chargers must precisely regulate the charging of such batteries.
Charging voltage must be precisely controlled in Li-Ion/Li-P battery chargers. Typically external circuitry is placed about Li-Ion/Li-P cells, to prevent failure. When protection circuitry fails, however, Li-Ion/Li-P cells can once again become unstable. There is thus a need for a means for testing safety circuits.